Automatic line testing and switching circuits



Mafch 19 .6

AUTOMATIC LINE TESTING AND SWITCHING CIRCUITS ART Dec 9' DELA y QUAL- SE (.5675 64 KC PF I 2 Sheets l PA, I

SELECL S FIG.

SELECT's lNl/E/V B. DYSAR 7 ATTORNEY OUTPUT 0 U TPU 7' OUTPUT ar h '19, 1946. B YSART j 2,999,990

AUTOMATIC LINE TESTING AND SWITCHING CIRCUITS:

Filed Dec. 9, 1945 2 Sheets-Sheet 2 FIG. 2

FIG. .3

A INE'IT POWER l nv ur POWER Agar Pom: IN [/5 N T OR' I 5. DKSART Arm/War Patented Mar. 19, 1946 AUTOMATIC LINE TESTING AND SWITCH- ING CIRCUITS Birney Dysart, Madison, .N. 1., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of 'New York Application December 9, 1943, Serial No. 513,591

' 13 Claims.

The invention relates to broad frequency band transmission systems, such as multichannel carrier wave signaling systems, and particularly to automatic line testing and switching circuits for use with such systems.

In such systems employed for transmitting signal waves over a long distance, it is customary to use a large number of repeaters .in tandem, some of which may be attended and others unattended. The failure or substantial impairment in transmission efiiciency of a single transmission element, for example, an amplifying vacuum tube or a line conductor, in a line section between :repeaters may result in complete failure or intolerable degradation of transmission over that line section. In certain carrier wave signaling systems, such a 'multichannel coaxial cable carrier signaling systems, in which a singl line pair or coaxial conductor is employed for transmitting several hundred signaling channels, such partial or complete failure may interrupt or seriously degrade transmission in a large number of si naling circuits, resulting in much inconvenience and substantial loss of time and revenue before the condition causing the failure is found and remedied. For that reason, it is customary to employ in such systems, two or more completely equipped parallel lines in each repeater section, only one of which is normally in working relation to provide through signal transmission, withsuitable switching circuits for substituting a spare line section in place of a working line section in which a transmission failure occurs.

My copending patent application, Serial .No. 495,989, filed July 24, 1943, which issued :as Patent No. 2,379,069 on June 26, 1945, discloses automatic switching arrangements for use with such a system, employing special relay circuits adapted for control by any one of a number of pilot waves of different frequencies outside the signal frequency rang continuously transmitted over the working and spare lines in 'a switching repeater section, when its transmission level deviates a given amount from normal level in either direction indicating serious line impairment,to continuously monitor each of thelines to determine if an impaired condition exists; to indicate the transmission condition of each line to an attendant; and to automatically shift signal transmission from an impaired working line to a spare line only if the latter is in tolerable working condition. y

An object of the invention is to improve automatic arrangements of the above-described general type particularly from the standpoint Jor I simplification and speed or operation. More specific objects are to continuously monitor the working and spare lines in the re-' peatercsections of a broad frequency band signal transmission system; *to operate suitable 'signal* ing apparatus indicating which of the lines'are" working and which are spare, and the condition of each line; and .to shift through signal transmission quickly .irom a working line found to'be substantially impaired to a spare line only if the latter is intolerable working condition. Another :objectis to provide regulating control of a switching device associated withaline 'tra'ns-- mitting wave energy only when the amplitude level of that wave energy .is .outside tolerable limits.

These objects are attained in accordance with the invention by simple pilot-controlled automatic circuit arrangements employing particular arrangements of electronic switching devices to provide'the required line switching and alarm indication within .a relatively short time interval after a line trouble conditionoccurs.

A feature of the invention is a control device which produces an appreciable output for applied alternating wave inputs within a given range of amplitude levels and substantially no output for alternating wave inputs of amplitude levels .aboveyand below that range. y The :various objects and features of. the inven"-- tion may be better understood from the following detailed description when read .in-conjunction with the accompanying drawings in which: Fig. l rshowsschematically a'switchin'g repeater section for one direction of transmission ,in-a wide band signal .transmissionsystem, suchqas a multichannel carrier telephone system, equipped with automatic line testing, switching and indi= eating arrangements embodying the invention; Fig. 2 shows schematically ,a control device of novel type .such as are used in the arrangements of theinvention shown in Fig. 1; and v Fig. 3 shows curves illustrating the operation of the control device shown in Fig. 2.

Fig. 1 shows one switchingrepeater section for the west-to-east direction of transmission in a wide band signal transmission system, such as a multichannel repeatered cable carrier wave signaling system, comprising the two one-wayllines LA and LB extending between a west repeater station and anreast repeater station at theiterminals of the section. It is understood-thatthe line may include any number of tandem-connected repeater spans containing any number of repeater ofiices which may be attended or unattended, each line being completely equipped with the amplifiers, associated gain regulating apparatus, equalizers and other equipment (only a portion of which is shown) required to provide a desired volume and quality of signal transmis sion over the switching section. Thelines LA' and LB are permanently connected through the balanced windings of the hybrid repeating coil HCw in energy transmitting relation with the output line LW of the preceding repeater switchingsection or carrier terminal station so as to be supplied in common from the latter line with equal energy portions of the, carrierfsignal frequency band containing the carrier signals of all signal channels to be transmitted.

If the switching repeater section shown in Fig.

l is the first one in the system for transmission in the West-to-east direction, so that the hybrid coil HCw is located at a terminal repeater station, pilot waves of frequencies, say 64'kilocycles and 2,064 kilocycles, on either side of the carrier signal band to be transmitted and .of equal,

initially constant amplitude levels, arecontin characteristic impedance of the incoming line'LW- which it faces, through the hybrid coil HCw. If

the switching repeater section illustrated in Fig;

1 is not the first switching repeater section for that direction in the system, the pilot waves 'may be supplied in a similar manner at the preceding terminal station or at the input of any preceding switching repeater section so that the pilot waves will be received over the line LW: and applied through the hybrid coil HCw in equal energy portions to the inputs of the lines LA and LB. 'In 1 that case, the usual line balancing network would be substituted for the pilot wave sources P1 and. P2 connected to the net side of the hybrid coil HCw. l

The outputs of the lines LA, LB are coupled at the output of the switching repeater section shown in Fig. 1 in conjugate relation with each other and in energy transmitting relation with the line LE leading to the next'succeeding switching repeater section or to a terminal repeater station, by the hybrid repeating coil HCE and associated line balancing network NE. i 4

The line LA includes near its output the dela network DN1 followed by the line equalizer E6311 and the line amplifier A1, shown as consisting of only one three-electrode amplifying vacuum tube stage having a parallel resistance-condenser grid biasing arrangement RC1 in its control grid circuit, but which may include any number. of vacuum tube stages required to provide the desired signal amplification. Similarly, the line LB includes near its output a delay network-BN2 followed by an equalizer EQ2 and a lineamplifier A2, similar to the amplifier A1, including .a three-, electrode amplifying vacuum tube stage having a parallel resistance-condenser grid biasing arrangement RC2 in its control grid circuit.

Connected across the'line LA at a point in the output of-the amplifier A1 is the input of a signal controlled switching circuit SWA including two former T1.

tandem-connected amplifiers A3 and At, which may be of the vacuum tube type similar to the amplifiers A1 and A2 in the lines LA and LB, and which, when both are operative, pass the portion of the signal and pilot wave output of line amplifier A1 diverted from the path LA into that switching circuit, in amplified form to the two diode rectifiers D1 and D2 having their inputs coupled to the output of the second amplifier A4 in the switching circuit by the common trans- Similarly, the input of a switching circuit SW13 is connected across the output of j the line LB in the output of the line amplifier A2,

that switching circuit including-the tandem-connected amplifiers A5 and As, which, when both are operative, pass the portion of the signal and pilot wave output of amplifier A2 diverted into the switching circuit from line LB, in amplified ficient to bias the latter amplifier to cut-ofi so as to block the line LB in its output. Similarly, the rectified voltage output of the diode rectifier D3 in switching circuit SWB applies across the resistance-condenser biasing arrangement RC1 a negative voltage to the control grid circuit of amplifier Ar in line LA, which, when completely built up, is suflicient to bias the latter amplifier to cut-ofi so as to block line LA in its'output.

The rectified voltage output of the diode rectifier D2 in switching circuit SWA controls the operation of a relay R1, and the rectified voltage output of the diode rectifier D4 in switching circuit SW1; controls the operation of a relay R2 which in turn controls the operation of a relay R3. The circuits controlled by the operation of the relays R1 and R3 in accomplishing the purposes of the invention will be described later in connection with a complete description of operation'of the system of Fig. 1.

Connected across the line LA at a, point near its output in front of the delay network DNl is the common input of the pilot-controlled control circuits P01 and P02, and connected across the line LB at a point near its output in front of delay network DNz is the common input of the pilotcontrolled control circuits PC; and P04.

The control circuit PC; includes in its input a filter PF1 for selecting from the portion of the wave energy applied to its input, that of the frequency 64 kilocycles received over the line LA from the pilot wave source P1 at the input of the switching section, and for suppressing applied wave energy-of other frequencies; an amplifier P A1 for amplifying the selected pilot wave energy; and a control device CD1 responsive to the amplified 64-kilocycle pilot Wave energy, only when its amplitude level rises above or falls below the range of pilot amplitude level considered tolerv able, due to serious line trouble conditions in the linejLA. over which the 64-kilocycle pilot wave passes, to bias the amplifier A3 in switching circuit SWA to cut-off. The control circuit PCs includes in its input a filter PFz for selecting from the wave energy applied to its input, that of the frequency 2,064 kilocycles received over the line LA from the pilot wave source P2 at the input of LE or-into the switching circuit SWB.

nals'over the switching section between the lines" LW and LE, the line LB then being'the'spa're line.

Half of the energy'of the carrier signalsreoeived over the line section LW and half of'the.

energy of the two pilot waves of frequencies 64 kilocycles and 2,064 kilocycles generated by the pilot wave sources P1 and P2, respectively, will pass through the hybrid coil HOW to eachiof the lines LA and LB, and will pass thereover respec tively through delay network DN1, equalizer EQ1 and line amplifier A1, and delay network 'DNz' and the equalizer. E'Qz, toward the line section- LE at the output of the switching section. A

portion of the signal and pilot wave energy will be diverted from the line LA into the input'oi switching circuit SWA, and, if the amplifiers A2 and A4 therein are both operative, 'as will be the case if the pilot energy diverted into pilot control circuits PC; and PC: is within tolerable amplitude level limits, with no appreciable impairment of transmission over the associated line LA, will pass in amplified form through these amplifiers to the diode rectifiers D1 and D2 and will be rectified by them. The rectified output of detector D1 maintains a blocking (cut-01f) bias on the line amplifier A2 in line LB and the rectified output of diode rectifier Dz holds operated relay R1, which in turn holds open the locking circuit for relay Ra.

Since amplifier m in line LB is biased to cutofi, the other half of the signal and pilot wave energy diverted into 'line LB will be prevented from passing over theoutput of that line'to line Therefore, nocut-ofi bias voltage will be supplied by rectifier D3 in switching circuit SWB to the am-- -plifier A1 in line LA, and the relays R2 and R3 in the output of rectifier D4 will be released,

causing the bias delay condenser C to be maintained connected in the biasing circuit for am-' plifier A1 in line LA. The line 'LA then will operate as the working line to transmit signals and pilot wave energy from line section LW to 'line' section LE, and line, LB will be the spare line disabled in' its output." If the manual-key TST is operated and relayRa is released, an energizing circuit from battery B1 will be' provided for lamp L1, and that lamp will light up to indicate that line LA is the working line and is'in tolerable working condition, whereas lamp L2 not supplied with battery will be extinguished, indicating to aniattendant that line LB is operating as the spare line.

Now, if the amplitude level of either or both of the 64 kilocycles and 2,064 kilocycle s pilots continuously transmitted over'the line LA and passing through the pilot filter PFi and amplifier to cut-off, thereby cutting oi the input to rectifiers D1 and D2 in switching circuit SWA. This will cause the blocking (cut-off) bias to be removed from the amplifier A2 in line'LB, and the relay R1 to release to close the break through its contacts in the locking circuit for relay Rs.

The unblocking of amplifier A2 in line LB will allow the signals and pilot waves received over that-line from the west line section LW, and the pilot wave sources P1 and P2, respectively, to be transmitted to the input of the switching circuit SWB and over the output of line LB through the hybrid coil HCE to the east line section LE.

If'line LB .is then in tolerable operating condition, as indicated by the pilot wave outputs of the fi l-kilocycle and 2,064-kilocycle pilot control circuits PC: and PC; producing constant outputs suchias to bias both amplifiers A5 and As in the switching circuit SWB to the operative condition, theportion of the signal'and pilot wave energy in the output of amplifier A2 diverted from line LB into that switching circuit, will pass in amplified form through the former amplifiers to the diode rectifiers D3 and D4 and will be rectified by them. The rectified output of rectifier Dawill buildup a blocking bias on amplifier A1 in line LA,-and the rectified output of rectifier D4 will cause the'operation of relay R2 and thus of relay R3.

The operation of relay R3 through its operated upper contacts will close a normal break in the locking circuitfor that relay enabling it to be locked-operated when relay Rx releases to close theother break in that looking circuit, from battery B2. The operation of relay R3, through its lower sets of contacts will disconnect the bias delay condenser C from across the biasing circuit of amplifier A1 in line LA and will connect it across the biasing circuit of amplifier A2 in line Thus, the output of line LB will be enabled and the output of line LA disabled so that line LB will then operate as the working line to transmit signals and pilot Wave energy from line section LW to line section LE, and line LA will be conditioned as the spareline disabled in its output.

Theoperation of relay R3 in response to the rectified output of rectifier D4, if test key TST is operated, will cause energizing current to be supplied frombatteryBi to the lamp L2 causing it to light up to indicate that line LB is now the working line and is in tolerable operating condition,'and energizing current to be cut off from the'lamp L1. causing it to be extinguished, indicating that LA is now the spare line.

If, as previouslydescribed, line LA is operat- 'ing as the working line and line LB as the spare line, and line LB fails causing operation. of one or both of its associated pilot-controlledcircuits P03 and PC4 to disable one or both of the amplifiers A5 and As in the switching circuit SWB associated with line LB, nothing happens as regards line switching. However, when the spare line LB fails, the resultant reduction substantially to zero of the output of the control device CD: in controlcircuit PCs, or of the output of the control device CD4 in control circuit CD4, or of the outputs of both of these control devices, causing the disablingof amplifier A5, amplifier As or both of those amplifiers in the switching circuit SWB, indicate the spare line failure to an attendant.

If, on the other hand, both lines LA and LB fail simultaneously causing both switching circuits SW3. and SW. to be disabled under control other -.tra'nsmissioncircuitso that for-normal signalztransmission conditions in said one circuit it is .operative to transmit signals from said source i .tofsaid output circuit and, the other transmission circuit is .prevented from doing so, and means ,zresponsive; to the occurrence of abnormal signal transmission conditions in, said one circuit, only if -q.normalfsigna1 transmission conditions exist in saidother circuit, for, so controlling the operation ,of the two switching devices that said other cir- ..;,Q11it.hec0mes operative to transmit signals from said source to said output circuit and said one circuit, is prevented from doing so. 7

$2.1m Combination, a source of signals, two

transmission circuits supplied in common from,

. said source; a common output circuit for said 7 transmissioncircuits, a signal-operated switching device connected to each transmission circuit,

=,wh.ich;when completely operated by signals in that circuit disables the other transmission circuit and ..v-.theswitching device connected thereto, means for :making the switching device connected to one of said transmissionlcircuits effectively faster in operation than the switching device connected to the other circuit so that for normal signal transa i mission conditions in said one circuit it is operative as axworking circuit to transmit signals from said source to said common output circuit and 4 the other transmission circuit is prevented from doing soand means responsive to the occurrence I ofabnormal transmission conditions in the trans- .,mission circuit operating as the working circuit to disable the switching device connected thereto so that said other transmission circuit is rendered operative as the working circuit to transmit sig-' nals. between said source and said common outi put circuit and the switching device connected to said other circuitholds the first transmission circuit and the switching device connected thereto disabledwhile said abnormal signal transmission conditionsin said first circuit continues. 3.-'I'he combination of claim 1, in which the I last-mentioned means 7 comprises means for con- --tinuusly transmitting a plurality of pilot waves --=of different. frequencies outside the signal irequency range over each of said transmission cir- 'cuits andmeans responsive to abnormal variation ofithe level of any one-of the transmitted pilot waves at a given point in the circuit over which they are transmitted to cause the switching device connected thereto to be disabled. 7 7

- 4; In combination, a source of signals, two transmission circuits supplied irom'said source,

- a 'common output circuit for the two transmission circuits, a signal-operated switching device "connected to each transmission circuit near its "output; which when completely operated by the applied signals from the connected circuit disablesT the other transmission circuit and the "switching device connected thereto, delay means normally connected in the switching device connected to one transmission circuit, rendering its operation slower than the switching device conneoted to the other transmission circuit so that p for normal signal transmission conditions in said a other transmission. circuit it is operative as a that the. occurrence of abnormal signal transmission conditions only in the transmission circuit aeoaooo operating as a working circuitmill ,resultinthat circuit being rendered inoperative and the other transmission circuit being renderedoperativeto transmit signalslbetweeng said source gandsaid common outputjcircuit' while: said abnormal signal transmission-continues and means responsive to the complete operation of the switching device connected to said one circuit for causing said delay means to be switched from that switching ,device to the switching device connected, to said other transmission circuit so as to render the latter switching device slower inoperation than the former switching device. '1 1 5. In combination, two transmission circuits fed from a common source of signals-and feeding a common output circuit, each-including a normally operative transmission device'near its output, a switching'circuit including one 'or more normally operative transmission devices, connected to each of said transmission circuits in the :output of the transmission device therein, andoperatively responsive to applied signals, when that transmission device is operative, to disable the output transmission devioesrin the other transmission circuit and thus to prevent .itransmission therefrom to said common output circuit, the two switching circuits normally having respectively dlfierent-time constants making one-effectively faster in operation than the other so that for'normal signal transmission conditions in thetransmission circuit to which said one switching circuit is connected, that transmission circuit is conditioned as an operative working circuit to transmit signals from said source to said outputcircult and the other transmission circuit as a spare circuit disabled in its output; and other means responsive toabnormalsignal transmission conditions. in either of said two transmission circuits for causing the switching circuit controlled therefrom to be disabled, whereby the occurrence of abnormal signal transmission conditions in the transmission circuit which at the time is conditioned as a working circuit to transmit 'to said output circuit, will resultin that transmission circuit being disabled in. its output and the other transmission circuit which at the time is conditioned as a spare circuit, being renderedo'perative as the working circuit to transmit't'o said output circuit, but only. if signal transmission conditions in said other transmission circuit are'riormal at thattime. i J V 6. The system of claim 5 which said other 'means comprises means for continuously trans 'mitting at least one pilot'wave of a frequency outside the signal frequency range over each of said transmission circuits, and control means connected to each of said transmission circuitsat an output point in front of the disabling point therein, controlled'by the applied pilot waveof that frequency and operatively responsive, only when its amplitude level is outside prescribed tolerable limits, such as would be caused by completeor partial transmission failure in' that transmission circuit, to apply a blocking'bias tea transmission device in the switching circuit connected ftothat transmission circuit. 7

7. The combination or claim 5111' which each of said transmission devicesin saidtwoftransmission circuits and in said switchin circuits is an electronic device having a control element. which is disabled by the application of a block ing bias to that control elementdn response to operation of the controlling switchi circuitpr said other means,respectiyely;fi H

8. The'combination "of claim 5 in which the transmission device in the output of, each oisaid transmission circuits is an electron discharge device. having; a control grid circuit, which is dis.- abled by the application, of a cut-off blasto its control grid, circuit in response to operation of the switching circuit controlled from the other transmission circuit, and the, switching'circuit controlled from the transmission. circuit normally conditioned as a workin circuit "being rendered faster in operation than that switching circuit controlled from the transmission circuit normally conditioned as a spare circuit, by the inclusion in the latter switching circuit of means for delaying the application of cut-off bias to the control grid circuit of the electron discharge device which it controls.

9. The combination of claim in which the output transmission device in each of said transmission circuits includes an electron discharge device having a control grid circuit which is disabled by the application of a cut-off bias to the control rid circuit of that electron discharge device, and said one switching circuit connected to the transmission circuit normally operating as the working circuit being efiectively rendered faster in operation than that switching circuit connected to the transmission circuit normally operating as a disabled spare circuit, by the normal inclusion in the latter switching circuit only of means for delaying the building up of a cutoff bias on the control grid circuit of the electron discharge device in the workin circuit, which said cut-off bias delaying means is transferred to said one switching circuit on operation of the other switching circuit to render the latter efiectively faster in operation, after said one switching circuit has been disabled in response to abnormal signal transmission conditions in the transmission circuit to which it is connected, so as to condition the other transmission circuit thereafter during normal signal transmission conditions therein, as the working circuit transmitting to said output circuit and the first transmission circuit as the disabled spare circuit during that time interval.

10. In combination, two line sections each including an output amplifier fed from a common source of signals of wide frequency range and feeding a common output line, a signal-controlled switching device connected across each line section in the output of its output amplifier and responsive to the signal output thereof, when that amplifier is operative, to disable the output amplifier in the other line section, the relative time constants of the two switching devices being selected so that under normal signaling conditions in one line section only the one switchin device connected thereto is completely operated, thus normally conditioning said one line section as the working line transmitting to said output line and the other line section as a spare line disabled in its output, means to continuously transmit a plurality of pilot waves of different frequencies outside or within the signal frequency range, but not interfering with the signal frequencies, over each of said line sections, a plurality of control devices respectively selective to a different one of said pilot waves connected across the output of each line section in front of its output amplifier, each operatively responsive only to deviations in the amplitude level of the selected pilot wave beyond tolerable level limits, such as would be caused by partial or complete failure of the associated line. section, to effectively disable the switching device controlled from that linesection, whereby operation oi-gany ofathe control devicesconnected to: a working line will, cause signal transmission to be eirectively transferred to the spare line but only if the latter is intolerable operating: condition,

11. Thecombinationof claim 10 in; whicheach of said control devices connected to each lin section includes. two oscillators. adapted for conrol by: the pilot w ve selected; thereby, in such manner thatv one oscillator produces an output only for pilot wave inputs to the control device of levels up to the lower of said tolerable level limits, which output holds the second oscillator inoperative to produce an output for such pilot wave inputs, and said second oscillator produces a constant output for higher level pilot wave inputs up to the higher of said tolerable level limits, and no output for still higher level pilot wave inputs, the output of said second oscillator bein so connected to the switching device controlled from the associated line section that the constant output of that oscillator for pilot wave inputs of levels between said tolerable limits will have no efiect on the operation of that switching device, whereas during periods of pilot wave inputs of levels outside said tolerable limits when said second oscillator produces no output, that switching device will be disabled.

12. In combination with a source of waves of a wide range of amplitudes, one oscillator having a control input controlled by the waves from said source in such manner as to tend to make said oscillator produce an output of appreciable power for wave inputs of all amplitudes up to a given limiting value within said range, and substantially no output for wave inputs of higher amplitudes, a second oscillator having a control input controlled by the waves from said source in such manner as to make said second oscillator produce an output of appreciable power for wave inputs of all amplitudes up to a second limiting value lower than that of said given value, and substantially no output for wave inputs of higher amplitudes, means to apply the output of said second oscillator to the control input of said one oscillator in such manner as to bias the latter oscillator to cut-oil while wave inputs of amplitudes up to said lower limiting value are being applied thereto from said source, thus providing output of one of said oscillators being coupled to said output circuit, a pair of potentiometers, the output of said rectifier being applied to the biasing input circuit of each of said oscillators through a dilferent one of said potentiometers so as to bias the oscillator in accordance with the voltage drop produced in the associated potentiometer by the rectifier output current, the resistance values of said potentiometers and their settings being selected so that said oneoscillator tends to produce an output of substantially constant power for all amplitude level values of the current supplied to said input circuit up to a given higher limiting value, and then cuts on so as to produce substantially no output for higher oscillator in such manner that the latter oscillater is biased to cut-oil during periods in which the'amplitude level of the current supplied to said input circuit is below said lower limiting value, thus producing in said output circuit an appreciable output for current inputs to said input circuit of amplitude levels ranging between said lower and said higher limiting values, and

substantially no output for current inputs of amplitude levels below and above said range.

' BIRNEY DYSART. 

